Magnet structure



March 27, 1951 5, LEVY 2,546,344

MAGNET STRUCTURE Filed Dec. 31, 1946 Ticrfi.

SIDNEY E. LEVY ATTORNEY INVENTOR Patented Mar. 27 1951 inure! STATESPATENT OFFICE MAGNET STRUCTURE I Sidney E. Levy, Brooklyn, N. Y.,assignor to University Loudspeakers, Inc., New York, N. Y., acorporation of New York Application December 31, 1946, Serial No.719,432

2 Claims. (Cl. 175-21) I have described a magnet of the plate typehaving doubly polarized magnetization and adapted to be utilized in aloudspeaker. My present invention is an improvement upon the structureshown in the above mentioned application and provides for a more evendistribution of the magnetic flux than could be achieved in thestructure shown in that application. This application is, therefore, acontinuation-in-part of my prior copending application above mentioned.

By plate magnet is meant a structure having at least one flat surfaceand wherein the magnetic orientation lies in substantially a plane whichis the plane of the structures flatness. This is to be distinguishedfrom a magnetic structure which is bent or curved or has a cylindricalor shell shape or one wherein the flux lines flow in more than oneplane, or where the flow is not generally parallel to the flat surfaceof the magnet.

It is an object of the present invention to provide doubly polarizedplate magnets, including bar magnets, of varying thickness, whereby theflux distribution in the magnet proper will be uniform.

It is another object of my invention to provide such a bar magnet andcooperating keeper or pole piece in which the bar magnet is shaped toeliminate unused portions and thereby concen trate the flux across themagnetic gap.

Other objects and features of the invention will be apparent when thefollowing description is considered in connection with the annexeddrawings, in which:

Fig. l is a side elevation of a variable thickness bar magnet inaccordance with my invention showing inner and outer pole pieces mountedthereon;

Fig. 2 is a top plan view of the structure of Fig. 1;

Figs. 3 and 4 are, respectively, a side elevation and bottom plan viewof the, structure of Fig. 1 showing particularly the mode of eliminatingsubstantially unused portions of the magnet Fig. 5 is a top plan Viewofa circular magnet in accordance with my invention; and

Fig. 6 is a side elevation of the circular magnet of Fig. 5.

Referring now to the drawings, there is shown at I 0 the magnet of myinvention having mounted thereon and centrally thereof an inner polepiece II and having likewise mounted thereon the outer pole piece I2,the said outer pole piece being provided with the circular'aperture I3forming with the inner pole piece II the usual nagnetic'g'ap I4.

In the construction indicated in my copending application abovementioned, the flux is concentrated in the area of the magnetimmediately beneath the inner pole piece II and becomes lessconcentrated as the periphery I5 of the magnet is approached. By mypresent invention, the magnet is made thicker at its center, so that thecross-sectional area of the magnet at the center point thereof issubstantially twice the crosssectional area at the outer edge I5. Inthis way, as will be seen by reference to the dotted lines in Fig. l,the flux concentration is substantially uniform throughout the magnet,and the entire strength of the magnet is utilized to produce a fluxacross the magnetic gap I4. In other words, it is possible to utilize amagnet of considerably lesser mass in producing the same result, or toproduce a much better result with a magnet of equivalent mass. 1

Referring now to Figs. 3 and 4, it will be seen that in this instancethe magnet II] of Figs. 1 and 2 has been cut away along its side edges,as indicated at I6 so that at its center, the magnet width isapproximately equal to the center pole diameter. Otherwise, the materialin these regions would be substantially useless, due to the fact thatthe flux circuit extends outwardly from the inner pole piece II alongcurved lines representing the pole piece diameter and does not takesharp bends such as would be required of any flux flowing through thearea which has been cut away. In order to compensate for thecross-sectional area of material removed, the magnet I II proper ofFigs. 3 and 4 is made thicker at its central part, and in a particularinstance in which the width of the magnet was one inch and the diameterof the inner pole piece II half an inch, the vertical dimension at theperiphery I5 of the magnet was made a quarter of an inch and that at itscenter point approximately an inch. By this modification thecross-sectional area of the magnet at its periphery is againsubstantially half the cross-sectional area at its center, and thusprovision is made for a uniform flux density throughout the doublypolarized magnet.

The variations in thickness and in width above described will realizethe maximum flux density in the air gaprin applications of a bar magnetpossessing one polarity at the center and the Qopposite polarity at itsperiphery. In these applications the magnetic flux density at the centeris twice that at any one end, hence the crosssectional magnet area atthe center should be double the area of one end.

In FigspdandQG-ithere is shownga circular magnet I! which is somagnetized as to have one polarity at its center and the oppositepolarity at its edges. In this form of the magnet f;mlV invention, themagnet is so designed that the ratio of the cross-sectional area of theperiphery l8 of the magnet to the cross+sectionalaarea ofthe annulussubtended by the circumference/of the center pole piece, to be usedtherewith, is in the neighborhood of 2:1, thusrassuringumifnrmdfil sitythroughout the magnet.

While I have described a preferred form-of .-my invention, it will beunderstood that alternate -;f qrn1s tmay :be devised without departingfrom ithe-spirit of theinvention. :Consequently, 71 Wish :to be limitednot {by the foregoing description, which was given :solely for r thepurpose of illustration, but onlyby the-appended claims.

:What is-claimedis:

1. A plate magnet generally rectangular in 11313.11 ,having one polarityat its center and the ,ppposite polarity at its ends, said :magnet beingrelatively thick at its centerand diminishing to ;,a pproximately halfthe thickness at the said ends,

i-REFERENCES CITED I116 .ifiollowing references are of record in thefile of this patent:

UNITED STATES PATENTS Number Name Date 204,141 Eaton May 28, 187871,033,610 ,Nash we a- July23, 1912 1,955 248 ,Messick M Apr. 1-7,.19341,986,856 Ringel rJan. 8, 1935 2,075,488 Wager Mar. 30,1937

"Number "Country Date 490,010 Great Britain Us--- Aug. 4, 1,938

